Ok. So Akuma. surprisingly this is super simple to pull off, even if it'll be tedious. obviously you need him unlocked. the first step is to taunt. press back+taunt. akuma will sit down
next, before he gets up, press down+taunt. i don't know the exact timing, but i find spamming it works.

he will remain seated and will pull out a rice ball (pictured below),

notice that the super art gauge gradually fills up with each bite. when he's done eating, he will declare "i have been satiated!!" his eyes will glow, and you now have a new set of toys.



pressing down twice, then two attack buttons (light+medium for attack 1, medium+heavy for attack two modern) or either two punches (standard, attack 1, so for standard it's down x2 then two punch buttons) or two quarter circle forward and a kick (standard, attack 2), will perform shin akuma's new supers.




now, this is an incredibly long animation, so the usefullness won't really be apparent. but, in training mode it is good fun to pul it off.